When temperatures are scorching, yellow-billed hornbills of the southern Kalahari Desert in southern Africa dilate blood vessels in their beaks to thermoregulate and cool themselves, according to a study published May 18, 2016 in the open-access journal. PLOS ONE by Tanja van de Ven of the Percy FitzPatrick Institute of African Ornithology, University of Cape Town, South Africa, and colleagues.

While mammals have sweat glands to keep their bodies from overheating, birds can rely on panting (evaporative heat loss) and dilation of their blood vessels (non-evaporative heat loss), especially in their beaks. . Toco Toucans are an example of the latter: their oversized nozzles account for up to 60% of their non-evaporative heat loss at air temperatures above 28 degrees Celsius. While not as extreme as toucan beaks, hornbill beaks are still quite large in relation to their body. To determine if hornbills could also use their bill for this purpose, the authors of this study increased the air temperature around 18 southern yellow-billed hornbills captured from the wild and followed their heat loss through thermal imaging. .

The researchers found that beaks accounted for up to 20% of non-evaporative heat loss in birds, and suggest that the benefits of beak heat loss in hot weather likely vary depending on where the birds live. In the rainforests where toucans typically live, for example, heat loss from the beak might be key, as humidity can make panting less effective. For southern yellow-billed hornbills living in the desert, heat loss from the beak could be significant because, unlike panting, it can help conserve scarce water.

Tanja van de Ven notes: “We have found that, like toucans, hornbills can use their beaks as a controllable heat radiator. We believe this could provide an advantage in the arid Kalahari by reducing the amount of water birds need for cooling.